This invention relates to an artificial cardiac pacemaker especially one in which the power consumption is extremely suppressed.
Most circuits in conventional artificial cardiac pacemakers are constructed from transistors, resistors and capacitors, wherein every operational function is secured by the combination of the elements.
This method requires, however, a rather long time and expense for inspecting the devices because the characteristics of each device, differ widely. Furthermore, the elements which define the circuit time constant, such as the generator and multivibrator, cannot be constructed without capacitors and resistors in addition to transistors.
Additionally, it is well know that capacitors are difficult to integrate and minimize by conventional fabrication techniques. The size of them is finitely limited, even though chip condensers are realized.
Cardiac pacemakers are known in which the stimulating current to the heart is decreased in a stepwise manner from a definite value to a threshold value at which the heart can firstly come to capture electrical cardiac signals and wherein such operations are cyclically repeated. In another application, the output level to the heart is determined by the value of a capacitor which is charged by paced QRS complex signals repeatedly caused by the output pulses. In this case, however, no stimulating pulse is given to the heart during the time between the last one pulse which is insufficient to be captured by the heart and the recovery to the former definite stimulating current, i.e., the time required for charging the capacitor. Thus the stimulation of the heart is extremely delayed. Moreover, rather higher capacitance should be available for discharging through the heart or reversely for fixing the stepdown intervals of stimulating current, and for holding the output level during the one pulse duration. As a result, capacitors should have higher capacitance and it is not yet possible to increase the capacitance without increasing the capacitor size and thus it is difficult to minaturize pacemakers utilizing such capacitors.